Several arboviral encephalomyelitis viruses, most importantly Eastern Equine Encephalomyelitis and Saint Louis Encephalomyelitis virus (EEE and SLE) cause sporadic epidemics in the human populations of the Southeastern US. It is generally believed that these epidemics are triggered by a combination of ecological factors that allow the viruses to become amplified in a zoonotic cycle and to then escape this zoonotic cycle to infect humans and domesitc animals (primarily horses). It is believed that both amplification and the escape from the zoonotic cycle require the concordance of several ecological factors. However, the factors that are necessary for this process, as well as many other factors involved in the ecology of transmission of these viruses remain poorly understood. These include the reasons for the seasonal pattern of the appearance of these viruses in the avian population, and the means by which the viruses are able to move from an avian epizootic to infecting humans. The overall goal of this project will be to elucidate ecological factors necessary for promoting viral enzootics, and to identify the ecological factors necessary to allow the viruses to escape the zoonotic cycle and infect humans and other mammals. The specific aims of this project will be: 1. To study the temporal and spatial pattern of enzootic encephalitis infection at several sites in Alabama and neighboring states using GIS, serological and PCR detection methods. 2. To utilize a newly developed method capable of identifying avian blood meals to the species level to study temporal and spatial changes in the feeding pattern of the enzootic and bridge encephalitis mosquito vectors. 3. To correlate the feeding behavior of populations of the enzootic and bridge vectors in each study with changes in abundance, behavior, reproductive stage, age classes present, or general physiological state of the endemic avian fauna.